A method that bonds substrates together so that the substrates face each other across an air gap has been used as a method for packaging an acoustic wave device. It has been known to provide a part of a bump on a dummy pad as disclosed in, for example, Japanese Patent Application Publication No. 2000-91880 (Patent Document 1).
The provision of the bump on the dummy pad inhibits the stress rupture of the bump due to the difference in linear thermal expansion coefficient. However, when the substrates are bonded together across an air gap, the peeling or rupture of the bump causes the bump to be electrically opened. The reduction of such a malfunction of the bump is insufficient in Patent Document 1.